The present invention relates to an Integrated Coal Gasification Combined Cycle Power Generator (hereinafter referred as IGCC.)
Reducing the amount of the fossil fuel used and improving system heat efficiency is desired in the latest steam-generated power-generator systems.
Coal, the fossil fuel used for steam-generated power-generator systems, is available in abundant amounts compared to petroleum or natural gas. Consequently, coal is cheaper than petroleum or natural gas. However, although long-term, stable supply is possible, coal burning results in the discharge of environmental pollutants, such as CO2 and SOx. For the above-mentioned reason, use of petroleum or the comparatively clean fuel from natural gas occupies the mainstream.
However, the danger of excessive dependence on petroleum as a source of energy was pointed out by the petroleum crisis of the 1970s.
Moreover, the estimated depletion years of a petroleum and a natural gas, quoting from xe2x80x9cComprehensive Energy Statistics of the Energy Agency, 1991xe2x80x9d, will be just 50 years. Considering this fact, long-term stable price and supply of a clean fuel, such as these fuels, is becoming hard.
Consequently, the practical re-use of coal fuel gas to a thermoelectric power system is being recognized once again considering that the possible depletion years will be more than about 300 years based on the estimated amount of coal deposits.
The IGCC which uses a coal-gasification syngas fuel, reduces environmental pollution by generating less CO2, SOx, NOx. Referring to FIG. 16, a conventional system of the IGCC is explained.
As shown in FIG. 16, the IGCC constitutes a coal-gasification system (1), a gas-turbine system (2), an exhaust heat recovery boiler (3), and a steam turbine system (4).
In addition, the exhaust heat recovery boiler can be substituted for a heat recovery steam generator.
The coal-gasification system 1 is provided with a coal supply portion 5, an oxygen system 6, and a coal-gasifier 7.
That is, a pulverized coal from the coal supply portion 5 and an oxygen gas from the oxygen system 6 are supplied to the coal gasifier 7, and a part of the pulverized coal is burned in the coal gasifier 7.
The remaining pulverized coal reacts according to the following formula, keeping the temperature above the melting point of coal ashes, in the range of about 1500 degrees C. to about 1800 degrees C.
A combustible coal gas which is composed of carbon monoxide (CO) as a major ingredient is refined as a result of this reaction.
CO2+C=2CO. 
The oxygen system 6 is provided with an air-compressor 9 driven by a motor 8.
That is, after the air-compressor 9 compresses an inhaled air, producing a high-pressure air, the air-compressor 9 separates the high-pressure air into an oxygen gas and a nitrogen gas.
After separation from the high-pressure air, the oxygen gas is supplied to a coal gasifier 7. The air-compressor 9 makes the oxygen gas so-called oxygen blown gas and combustible coal gas is refined in the coal gasifier as mentioned above. After separation, the nitrogen gas is supplied to the gas-turbine system 2.
Moreover, the coal-gasification system 1 is provided with a cooler 10 and a gas clean-up unit 11.
A combustible coal gas refined in the coal gasifier 7 is cooled to about 400 degrees C. in the cooler 10. Then, the combustible coal gas is supplied to the gas-turbine system 2 as the clean coal gasification syngas fuel, after the removal of impurities, such as sulfur and dust, by the gas clean-up unit 11.
In addition, the cooler 10 cools the combustible coal gas by using cooling water from the steam turbine system 4. Since the cooling water is recovered again in the steam turbine system 4, the effective practical use of heat can be attained.
The gas-turbine system 2 is provided an with air-compressor 12, a gas turbine combustor 13, a gas turbine 14 and an alternator 15.
The air-compressor 12 supplies high-pressure air to the gas turbine combustor 13 which is combined with nitrogen gas from the oxygen system 6 and clean coal-gasification gas from the gas cleanup unit 11.
While the gas turbine combustor 13 dilutes the coal gasification syngas fuel with the nitrogen gas, an expansion work is performed in the gas turbine 14 by using the combustible gas.
An alternator 15 is driven by the driving torque generated by the expansion work. Moreover, the combustible gas which completed the expansion work in the gas turbine 14 is supplied to the exhaust heat recovery boiler 3 as an exhaust gas.
The exhaust heat recovery boiler 3 include a heat exchanger (16), which constitutes a super heater, an evaporator and an economizer. Moreover, the exhaust heat recovery boiler 3 uses the exhaust gas supplied from the gas turbine 14 in the gas-turbine system 2 as a heat source. That is, in the exhaust heat recovery boiler 3, a condensate/feed-water supplied from the steam turbine system 4 performs heat exchange in the heat exchanger 16, as a result, steam generated in the heat exchanger 16 is supplied to the steam turbine system 4.
The steam turbine system 4 is provided with a steam turbine 17, an alternator 18, a condenser 19 and a feed-water pump 20. The turbine working steam is made from the steam generated in the exhaust heat recovery boiler 3 and the steam from the cooler 10 in the coal-gasification system 1. Further, the turbine working steam supplied to the steam turbine 17 drives the alternator 18 by the driving torque generated through performing expansion work.
After performing the expansion work, the turbine working steam (an exhaust gas) is condensed to be used as the condensate/feed-water in the condenser 19. A part of the condensate/feed-water is supplied to the cooler 10 through the feed-water pump 20, then, the remainder of the condensate/feed-water flows back to the exhaust heat recovery boiler 3.
Thus, the IGCC, consisting of the coal-gasification system 1, the gas-turbine system 2, the exhaust heat recovery boiler 3 and the steam turbine system 4, uses the clean and refined coal gasification syngas fuel from the coal gasification system 1 as the gas-turbine working gas. In so doing, the IGCC improves system thermal efficiency and produces low Nox emissions by combining the xe2x80x9cBrayton Cyclexe2x80x9d of the gas-turbine system 2 and the xe2x80x9cRankine Cyclexe2x80x9d of the steam turbine system 4.
Although the conventional IGCC shown in FIG. 16 uses the coal gasification syngas fuel, a clean fuel, and produces an NOx concentration within regulatory limits, there are some problems.
One of the problems is related to the improvement in the system thermal efficiency.
In the IGCC, if the gas turbine 14 has a gas-turbine working gas temperature of 1300 degree-C. class, the system thermal efficiency is increased by more than 40%, according to xe2x80x9cOutline of New Energy Conversion Technologies: The Heat Transfer Society of Japan, 1996xe2x80x9d.
Elevating the system thermal efficiency by more than 40% is dependent on a cooling technology applied to a high-temperature section of the gas-turbine combustor 13 and a high-temperature section of the gas-turbine 14, such as a liner of the combustor, a gas-turbine nozzle blade, gas-turbine rotor blade and a gas turbine rotor.
As is generally known, in this kind of a system, the higher a gas-turbine working gas temperature rises, the more the system thermal efficiency improves.
However, a super alloys applied to a high-temperature section of the gas-turbine system has as a characteristic an allowable temperature of at most 900 degree C. For this reason, to keep the strength of the high-temperature section within the allowable temperature on the condition that the gas-turbine working gas temperature is made to be high temperature, the gas-turbine nozzle blade and the gas-turbine rotor blade should be cooled as described below.
For example, a part of a high-pressure air generated in the air compressor 12 in the gas-turbine system 2 is extracted, and the gas-turbine nozzle blade and the gas-turbine rotor blade are cooled by applying the extracted high-pressure air to a forced convection cooling method, a film cooling method and a impingement cooling method.
However, cooling the high-temperature section of the gas-turbine system 2 by combining the above-mentioned methods is already coming to the limit of system thermal efficiency. That is, as the gas-turbine working gas approaches the allowable temperature limit, the amount of the high-pressure air used to cool the high-temperature section of the gas-turbine system 2 must increase in accordance with raising the inlet firing temperature of the gas turbine.
However, this increase of the high-pressure cooling air supplied to the high-temperature section of the gas-turbine is not contributed to the expansion work of the gas turbine 14. Therefore, the system thermal efficiency drops (deteriorates).
Moreover, although the coal gasification syngas fuel refined in the coal-gasification system 1 is a clean source of energy, it does contain some impurities, such as dust.
Further, even if a suitable combination among the forced convection cooling method, the film cooling method and the impingement cooling method, was available, a cooling performance as predicted by calculations could not be obtained because the impurities adhere to the gas-turbine nozzle blade and the gas-turbine rotor blade.
Because of the above-mentioned problems associated with cooling technology that supplies high-pressure air to the high-temperature section of the gas-turbine, a new alternative cooling technology to replace the high-pressure air is needed to improve the system thermal efficiency.
It is an object of this disclosure to provide embodiments of the inventions described herein which overcome one or more of the disadvantages of the related art described above.
In accordance with the foregoing objects an embodiment of the invention provides an integrated coal gasification combined cycle power generator which comprises a coal gasification system in which a combustible gas is produced from coal. The combustible gas produced in the coal gasification system is supplied to a gas turbine system. A gas turbine in the gas turbine system performs expansion work using the combustible gas and supplied the exhaust gas generated therefrom to a heat recovery system. The heat recovery system uses the exhaust gas supplied from the gas turbine as a heat source and supplies the steam generated in the heat exchange to a steam turbine system. The steam turbine system performs expansion work on the steam generated in the heat recovery system. The steam turbine system comprises a condenser used to condense steam from the steam turbine to water. The condensed water is supplied to a heat exchanger in the coal gasification system where it is heated to steam. The steam is then supplied to at least one section of the gas turbine system which is at a temperature higher than the temperature of the steam for the purpose of cooling that section. A higher-temperature steam is recovered from the high-temperature section of the gas turbine system and may be supplied to the heat recovery system or to the steam turbine.
Another embodiment of the invention provides an integrated coal gasification combined cycle power generator similar to that described above. In this embodiment, however, the steam from the coal gasification system is then supplied to a driving turbine which is adapted to power an air compressor.
Yet another embodiment of the invention provides an integrated coal gasification combined cycle power generator in which the heat recovery system performs heat exchange using the exhaust gas supplied from the gas turbine as a heat source and water to cool the exhaust gas. The steam generated therefrom is supplied to at least one section of the gas turbine system which is at a higher temperature than the steam. A higher-temperature steam is recovered from the high-temperature section of the gas turbine system and may be supplied to a coal gasifier in the coal gasification system.
A further embodiment provides an integrated coal gasification combined cycle power generator where nitrogen gas generated in the coal gasification system is supplied to at least one high-temperature section of the gas turbine system, producing a higher-temperature nitrogen gas. The higher-temperature nitrogen gas is recovered and supplied to a gas turbine combustor in the gas turbine system.
Also provided are methods of improving the system thermal efficiency of IGCC, such methods comprising use of the IGCC system described herein.